The present invention relates generally to methods and apparatus for cementing a well; and, more specifically, relates to methods and apparatus for multiple stage cementing particularly useful in cementing operations performed within an existing casing string; otherwise known as "secondary cementing" operations.
Secondary cementing procedures are utilized in wells during their productive lives, such as remedial cementing and repairs to existing cemented areas. This may be necessitated by a number of occurrences. For example, the inside surface of an existing casing string will often corrode or otherwise deteriorate over time, thereby decreasing fluid flow through the string. In addition, the corrosion may cause the casing string to become fluid permeable, thereby leading to fluid leakage. At such times, secondary cementing may be utilized to repair the deteriorated section of casing. In such operations, when the well cannot be cemented from the bottom of the casing, it is often preferable to cement the annulus in two or more stages. For example, two stage cementing may be necessitated when the formation will not support a column of cement slurry over the vertical zone to be cemented.
Conventional multi-stage cementing tools have suffered from the deficiencies of either being too large in diameter to be satisfactorily utilized in workover operations, or of having components which are relatively difficult to drill out to provide an optimally open bore through the casing once the operation is completed.
Accordingly, the present invention provides a new multi-stage cementing tool and system configured to provide an optimally minimized outer diameter, and having internal components adapted to facilitate drilling out of the components facilitating the establishing of a full open bore after the cementing operation is completed.